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Canon XH Series HDV Camcorders
Canon XH G1S / G1 (with SDI), Canon XH A1S / A1 (without SDI).


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Old August 9th, 2007, 03:34 AM   #1
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A strange effect

I have been using the XH A1 for about a month and am generally satisfied with the camera, although I still have a strong loyalty towards my XL1s.

I shot a wedding recently on the XH A1 and noticed a slight popping of focus. A shot of the groom talking to camera displayed slight focus jumps, which seemed to last for one or two frames. I put this down to oversensitive autofocus and thought no more about it.

Yesterday, I used the camera to produce a video of someone talking to camera, this was under studio lighting conditions (1/50 at f4 16:9 SD, PAL format) and I had the focus set to manual. The shots are razor sharp, excellent! But when the subject moved his head, (nothing excessive, just normal head movement), the shot popped out of focus for one or two frames. The out of focus bits are just movement of the head

I have never experienced before using the XL1s, only on the XH A1.

I have put this down to one or two possibilities.

1. The shutter speed is too slow, although 1/50 does seem to be the accepted default.

2. The MPEG 4 compression. When a subject is static the compression is fixed, when it moves a greater amount of compression is applied.

The XL1s doesn't use MPEG 4 compression, this why I haven't seen it before.

Can anyone shed any light on this, or have I missed something in the setting up that should have been applied.

Many thanks.
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Old August 9th, 2007, 03:52 AM   #2
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I have just seen this in another post.

"Hi John. I moved from XL2 to A1 last december, and I totally agree with you that the XL2 is better for SD. The pictures are somehow more solid with the XL2 and don't have that shifting/smearing of fine details that happens sometimes with the A1 when you move the camera."

Does this smearing (Focus popping) only happen in SD?
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Old August 9th, 2007, 05:35 AM   #3
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High coring settings will kill detail and/or NR1 settings can cause smearing. Maybe that's what you're seeing?

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Old August 9th, 2007, 06:23 AM   #4
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Thanks, I have just checked these settings and they are both set to 0
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Old August 9th, 2007, 09:32 AM   #5
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Mpeg 2 not 4

All HDV is Mpeg 2 M2t format the smearing sounds to me like your camera is experiencing drop frames or data rate problems. Or you could have a problem with the tap you are using.

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Old August 9th, 2007, 09:49 AM   #6
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This is not a dropped frame issue or a focus issue, it is smearing or movement artifacting issue. You can tell by only the head getting the out-of-focus loo and the fact that you had autofocus turned off.

Recheck your settings and try again. Is the head movement fast or slow? I would think that 1/50 would be fine, but of course that depends on the speed of the movement. Cheat and put it on full auto and try it!

Last thing to check, what does the footage look like of the camera? Or, does the problem just show up on the monitor you are using.

Best of luck---Mike
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Old August 9th, 2007, 09:59 AM   #7
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Happens in SD mode?. Compression is intra-frame, not inter-frame. It is DV not MPG

Is this mainly apparent in stills or slow-mo playback, or watching full rate video as well?

My first guess would it is an artifact of motion with a slowish shutter speed.
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Old August 9th, 2007, 10:22 AM   #8
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Thanks for the replies.

I am looking at the footage on both a 20" Sony Bravia LCD TV and a JVC CRT monitor.

The footage is just normal video, not slow motion.

I would use a faster shutter speed, but have to stay with 1/50 using the daylight tubes (otherwise I get colour shift due to the phasing of the tubes - this was dealt with a while back). The outdoor video was shot using Av and I guess the camera defaults to 1/50 shutter speed.
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Old August 10th, 2007, 07:53 AM   #9
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Just a pre-coffee thought...

If the camera is on a tripod, try deactivating the image stabilization.
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Old August 10th, 2007, 01:23 PM   #10
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The image stabilisation was not in operation.
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Old August 10th, 2007, 01:52 PM   #11
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Can you post stills of the two frames with the issue?
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Old August 12th, 2007, 08:36 AM   #12
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Don,

Thanks for asking. I have just been through the footage on my JVC monitor and can't seem to see any difference between the frames. Yet when I view the footage on my Sony Bravia set then it has the focus shift problem. I wonder if it is something to do with LCD refresh rates.

I will do some more experimenting and try to get to the bottom of this.
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Old August 12th, 2007, 11:48 AM   #13
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interlacing issue?
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